It is conventional in two-group zoom lenses used for digital still cameras, surveillance TV cameras and similar imaging devices that use an imaging element, such as a CCD or a CMOS, to use plastic lenses that can be easily mass produced and are light in weight in order to meet the requirements of miniaturization, weight reduction, and cost reduction. Because the correction of chromatic aberrations as well as the compensation for variation in focal length of zoom lenses due to the variation in refractive index with temperature that occurs with plastic material are difficult to achieve, techniques have been proposed to resolve these problems by using aspheric plastic lens elements as set forth, for example, in Japanese Laid-Open Patent Application 2001-021806. In such a two-group zoom lens, it is common to perform focusing by moving the object side lens group of the two-group zoom lens. However, such conventional two-group zoom lenses using plastic lens elements leave much room for improvement in terms of miniaturization, weight reduction, and cost reduction.